Chance Cubes are items that appear in Super Mario Galaxy 2. They are found on Starship Mario and in bonus rooms located in several galaxies. Chance Cubes resemble dice, but each side shows either a 1-Up Mushroom, a coin, a Star Bit or Bowser's emblem. When Mario hits it, the cube flies back and lands in a similar fashion to a Dice Block. Whatever image is facing up determines what Mario will earn.

If a 1-Up Mushroom is shown, Mario earns a 1-Up Mushroom. If the coin side is facing up, the block bursts into ten coins. If the Star Bit side is facing up, Mario earns a single Star Bit. However, if the Bowser emblem shows up, a Goomba appears.

Chance Cubes can be accessed on Starship Mario via two Lumalees in a Warp Pipe next to the ship's "ear", once certain tasks are complete. Their Chance Cubes are different, allowing Mario to get either a Star Bit or one, three or five 1-Up Mushrooms. One Lumalee asks for 30 Star Bits to transform into one cube; the other one asks for 100 coins to transform into five cubes.

The Co-Star Luma can also spin Chance Cubes. Rolling into one as Rock Mario, burning it with a fireball as Fire Mario, hitting it with a Double Kick, rolling a snowball towards it, or shooting one with a Star Bit also activates it, as does riding Yoshi and doing a spin attack. Moreover, if Mario uses a Spin on the cube when it is still rolling it stops instantly, making it easier to get the desired item. This technique can even cause the cube to stop in midair with precise timing.

When rolled, the player will hear a snare drum roll, ended by a cymbal crash once it has landed on an image. The longer it takes for the picture to reveal (an example such as when it's rolling down a big hill), the longer the snare drum roll sound will be, and later the cymbal crash is heard. But the faster it reveals, the shorter the sound, and the sooner the cymbal crash sound is heard. Sometimes a few snare drum beats can be heard when spinning multiple chance cubes, during the drum roll sound.